The need to monitor and control chemical exposure has increased with concerns about the hazards imposed by chemicals in the environment. Exposure to airborne chemicals is especially hazardous since inhalation is the most efficient mechanism for absorption of chemicals by the body. Accordingly, limits have been placed by regulatory authorities on permissible concentrations of toxic chemicals that may be present in the environment.
In the workplace, where a variety of chemicals are commonly used, more than 600 Permissible Exposure Limits ("PEL") have been established by the U.S. Occupational Safety and Health Administration ("OSHA") under the Occupational Safety and Health Act of 1970. Additional limits to chemical exposure in the general environment have also been set by the U.S. Environmental Protection Agency in the Clean Air Act of 1968.
Since concentrations of chemicals in the workplace may vary from time-to-time and from place-to-place, air monitoring is required by the OSHA to determine whether a workplace is in compliance with Permissible Exposure Limits. Since the primary hazard in such circumstances is inhalation by workers, U.S. regulations specify that air samples taken to demonstrate compliance with Permissible Exposure Limits must measure Time-Weighted Air Concentrations in the worker's "breathing zone," i.e. near to the nose and mouth.
In order to comply with this requirement, air monitoring devices should be light and compact enough to be worn by the worker during work tasks without hampering the worker or inducing any changes which may affect the air sampling process. Ideally, such a "personal monitor," as they are called, should be light and compact enough that the person being monitored quickly loses awareness that a sampling device is being worn.
Environmental air sampling can use pumps to draw air samples though collection devices for analysis. For example, U.S. Pat. No. 5,000,052, issued Mar. 19, 1991, inventor Sitin, describes a sampler device, such as for area monitoring during asbestos removal. However, this sampler device uses area sampler pumps, which are usually relatively large and stationary and are designed to sample much larger volumes of air at high flow rates than personal sampler pumps, which are designed to be worn by an individual being monitored.
Pumps are known and used with monitors worn on the person. Thus, traditional personal air sampling methods developed by the National Institute for Safety and Health ("NIOSH") required belt-mounted air sampling pumps weighing upwards of two pounds, which draw the air sample through a glass tube attached to pocket or lapel. However, such devices have proved to be cumbersome and expensive to use.
Due to their small size (typically, the size of a business card and weighing less than one ounce) and ease of use, diffusive samplers have become more popular than traditional methods using pumps as diffusive samplers permit more convenient personal sampling in compliance with OSHA requirements at a lower cost and with less disruption of the worker performing his/her tasks.
Air monitoring devices which collect a sample via gaseous diffusion have permitted a dramatic reduction in the size of personal samplers. An early personal monitor based on diffusion is described by U.S. Pat. No. 3,985,017, issued Oct. 12, 1976, inventor Goldsmith. Subsequent descriptions of personal air monitoring devices are contained, for example, in U.S. Pat. No. 4,235,097, issued Nov. 25, 1980, inventor Kring et al.; U.S. Pat. No. 4,265,635, issued May 5, 1981, inventor Kring; U.S. Pat. No. 4,348,358, issued Sep. 7, 1982, inventors McKee et al.; and U.S. Pat. No. 4,790,857, issued Dec. 13, 1988, inventor Miksch.
While diffusive samplers, or "passive" samplers as they are often called, have become popular for monitoring chemically exposed workers, sampling pumps have not disappeared due an advantage they retain, namely, that sampling pumps can normally sample at a higher rate (volume of air per unit time) and, consequently, given a comparable sampling time, sampling pumps can normally detect lower levels of air contaminants than diffusive samplers. Presently, as regulators seek to lower chemical exposure levels, the ability to detect and measure lower contaminant levels has become ever more important.